Mechanical Evaluation of Internal and External Fixation for Metacarpal Fractures

The purpose of this study was to compare fixation techniques for metacarpal fractures under the most and least mechanically demanding situations: bone contact and no bone contact and to test the potential role of soft tissues in providing a mechanically significant tension band to support the fixation. Two hundred fifty-eight (258) human metacarpals fixed in formalin (some dissected free of soft tissue and others in intact hands) were mechanically tested in 3 point, apex dorsal bending with midshaft transverse osteotomies to compare five (5) types of internal fixation and nine configurations of external fixation. In addition, eighty-four (84) proximal phalanges were fixed with both dorsal and lateral plates and tested in 3 point bending with and without soft tissue support. Reduction with end to end contact was obtained in the first series and a 3 mm. gap at the osteotomy site was obtained in a second series. The dorsal plate provided the greatest rigidity and strength with bone contact. External fixation was at least as strong and rigid as wire internal fixation. All configurations of external fixation were were stronger and more rigid than internal fixation with agap at the fracture site. Double frame configurations were statistically significantly more rigid and stronger than single frames in almost all configurations tested and pin placement nearest the A-P plane were the most rigid and the strongest. More compliant fixation systems were supplemented the most in by intact soft tissues, but all fixation systems incrested in strength and stiffness with intact soft tissues. Lateral plates were comparable in strength and stiffness to dorsal plates in dorsal bending only when soft tissues were intact.